Then, earlier on, you could just type:
subdomain2.subdomain.domain.com

in the creation of subdomains on the domain.com

Some time (was it back in the Year 2006?), this possibility was removed, so now you have to:
subdomain2[subdomain.domain.com]

instead!

Then, of course, this happens:
Error from domain wrapper: subdomain2.subdomain.domain.com is owned by another user.

This has happened me twice during the last few Days, and as I don't have root access (I am leasing server space), I can't do any thing with it myself!!

When you delete a subdomain (subdomain2 in this case), an extra line is added to a config file somewhere outside my very own control, and then I have to ask the web hosting company to do this job for me.